Deadly earth­quakes and tsunamis could be spot­ted min­utes sooner by read­ing tiny changes in grav­ity

Sunday Times (Sri Lanka) - - INTERNATIONAL - By Harry Pet­tit

As many as 10,000 peo­ple die each year in earth­quakes, with up to 3.1 mil­lion quake-re­lated deaths pre­dicted in the com­ing cen­tury. Once an earth­quake has been trig­gered deep in the Earth's crust, each minute that passes is vi­tal to those left un­aware in its im­pact zone.

Now sci­en­tists say that watch­ing for changes in grav­ity could save lives by warn­ing peo­ple far ear­lier of the location and mag­ni­tude of big earth­quakes.

Cur­rent early-warn­ing sys­tems rely on de­tect­ing seis­mic waves, which travel around seven to eight kilo­me­tres per sec­ond. Grav­ity sig­nals fire through the at­mos­phere at more than 300,000km per sec­ond, mean­ing they could be used to catch earth­quakes up to 40,000 times faster.

The re­searchers, from the Paris In­sti­tute of Earth Physics, came to their con­clu­sion us­ing data col­lected dur­ing Ja­pan's 2011 To­hoku earth­quake. The 9.1 mag­ni­tude quake killed more than 15,000 peo­ple, and left over 300,000 home­less.

The team looked through seis­mic data fol­low­ing the quake for a grav­i­ta­tional sig­nal that could have fore­shad­owed the event. Im­me­di­ately fol­low­ing the quake, while seis­mic waves were still on their way to warn­ing sta­tions across Asia, seis­mo­graphs recorded a grav­ity change re­flec­tive of the event's deadly mag­ni­tude, the re­searchers re­port. These sig­nals con­sis­tently ar­rived at seis­mic mon­i­tor­ing sta­tions be­fore their seis­mic wave coun­ter­parts.

If this ap­proach had been avail­able in 2011, the fact the To­hoku quake had a mag­ni­tude higher than 9 could have been de­tected in min­utes, the sci­en­tists claim. In­stead, the near-real-time mag­ni­tude pro­vided by the Ja­pan Me­te­o­ro­log­i­cal Agency was 7.9. This was then cor­rected three hours later to 8.8, which was an­other un­der­es­ti­ma­tion.

Go­ing for­ward, the Paris team says these prompt 'elasto-grav­ity' sig­nals could be used to make ear­lier es­ti­mates of large earth­quake mag­ni­tudes. The grav­ity changes or 'elas­tic waves' gen­er­ated by earth­quakes are a well-known phe­nom­e­non.

Last year, a sep­a­rate group of re­searchers from the Paris In­sti­tute showed it might be pos­si­ble to de­tect the size of earth­quakes by mea­sur­ing these elas­tic waves. 'The 2016 study was able to show evi- dence of a sig­nal. But be­cause this ex­is­tence was proved through a sta­tis­ti­cal anal­y­sis, it was not ex­actly the smok­ing gun we would have hoped for,' Dr. Martin Vallee, lead re­searcher of the new pa­per, said. 'In the present study, the early sig­nals re­lated to grav­ity are ob­served con­sis­tently at sev- eral lo­ca­tions. Ad­di­tion­ally, and im­por­tantly, we are now able to fully un­der­stand the ori­gins of these sig­nals and to model them ac­cu­rately. Our study fi­nally, con­cretely shows how these sig­nals are sen­si­tive to earth­quake mag­ni­tude, which of­fers a new way to eval­u­ate it very early after the earth­quake oc­cur­rence.'

The dev­as­tat­ing To­hoku-Oki earth­quake hit Ja­pan in 2011

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